Testing is an important part of the manufacture and use of printed wiring boards (PWBs). PWBs provide mounting and interconnection for integrated circuit chips in many electronic devices and systems. As the number of chips interconnected increases, it is important to be able to test the operation of chip components and the resulting circuit.
Unfortunately, increasing component density has also made it more difficult to test the components on the device area of a PWB. The device area is the portion of the PWB populated with various active and passive electronic devices. With increasing density, this area is filled, with little space remaining for testing points.
The conventional PWB has a device area including an array of testing points and is tested using a "bed of nails" probe. These probes have relatively "long nails" that must extend across the PWB without interfering with the devices mounted thereon. PWB stretch and shear, contact size limitations, and the length of the nails, all substantially reduce the accuracy of nail/contact registration and produce mediocre contact performance.
Recent technological trends also call for PWBs that operate at higher signal frequencies, typically in the radio frequency (RF) range. These PWBs require in-circuit, functional, and prototype RF testing to determine electrical characteristics across a circuit path of interest. Providing PWB testing points for RF probing is particularly difficult even with relatively short traces leading from the circuits to the contacts or probe pads. Indeed, designers often eliminate these contacts and their associated traces in order to speed up the PWB design process. Furthermore, at radio frequencies, signals travel on the surface of the conductor. Consequently, the mediocre contact performance inherent in bed-of-nails probing is especially detrimental.
RF testing points provided within the device area of a PWB are often blocked or covered by RF shields or housings installed to the PWB, making the testing points inaccessible for RF functional testing. If the shielding or housing is removed to gain access to the testing points, the circuit of interest often becomes inoperable. Inaccessible testing points also extend the duration of the prototyping phase because debugging becomes more difficult. Consequently, the PWB's time-to-market is substantially increased.
Accordingly, there is a need for a PWB with improved probing for in-circuit, functional, and prototype testing.